By Matt Miller, senior science writer
Standing on the bow of the boat, Steve Herrington exuded the excited energy of a kid reeling in his first fish. Or perhaps a more scientific version of the Crocodile Hunter, bubbling with intensity. Net in hand, he scooped up shad — a migratory fish species — quickly examining them before passing them off to fellow researchers.
As covered in yesterday’s blog, last year I spent a day with Steve on Florida’s Apalachicola River looking at Alabama shad, a fish that researchers hoped would benefit by a practice known as conservation locking—basically allowing fish to pass through dams by using the same lock system that enables ships to pass.
Herrington was then director of freshwater programs for The Nature Conservancy’s Florida program (he now holds the same position with Missouri). At the time, conservation locking on the Apalachicola seemed to hold great promise for shad, a migratory species. He estimated that conservation locking could result in a returning population of 60,000 to 75,000 shad, indicating a steady increase.
Fast forward a year later. Herrington is on the phone, and that same infectious enthusiasm is literally bubbling over. “Great news!” he exclaims.
And indeed, his research has yielded surprising results. Those initial estimates of 60,000 shad? Way low. Estimates now showed a 122,000 fish increase, with as many as 280,000 total shad now in the system.
“We can now confidently say that conservation locking works, and we’re seeing a substantial bump in the population,” Herrington says. “I don’t know that there are any other data out there that so convincingly demonstrates such effectiveness.”
But how do researchers know this huge fish increase was related to the dam passage? Couldn’t the fish just be spawning below the dam?
The research has those questions covered, too. Part of the project was analyzing otoliths—the ear bones in fish—to determine where fish were born. Otoliths are like a tree’s rings, showing each year of a fish’s life. These rings incorporate trace chemicals of the waters where the fish have lived, enabling researchers to accurately track where a fish was born.
The results of the analysis: 97 percent of the shad population was born upstream of the dam.
The shad were passing the dam. They were breeding. And thriving.
Alabama shad once migrated in huge numbers up many southern rivers, and as far north as Iowa. Could conservation locking help restore Alabama shad more broadly across their range? Herrington has high hopes, and is currently working with other conservationists and the Corps of Engineers in ensuring low-tech, low-cost practices like this are authorized.
“There are rivers where shad still run, but they eventually bump their heads into a dam and can’t go farther,” Herrington says. “We have a simple way to provide effective fish passage.”
Shad once played a huge role in river ecosystems. A return of their numbers could have implications for other species. Freshwater mussel populations, for instance, have declined precipitously. Many mussel species begin their larval stage by living in fish gills, and there is some indication that some might require shad. Could more shad mean more mussels?
Similarly, young shad might provide more food for largemouth bass. In this part of the country, bass fishing is often mentioned in the same reverent tones as religion. Could more shad mean more and bigger bass?
These and other subjects are all subject to ongoing research. “We’re gathering data that show how the recovery of shad can lead to the recovery of mussels and recovery of ecosystems, and benefit the region’s recreation and economy,” says Herrington.
And there’s still work to be done: despite the great success of conservation locking, only about 35 percent of shad are able to pass through. “We’re making the best of the situation. We are seeing large increases in population when 35 percent can get through,” says Herrington. “Just think what the population boost would be if we could get 60 or 70 percent through the dam.”
Herrington and other conservationists are now intent on working with the Corps of Engineers, who regulates these dams, to demonstrate how little tweaks in operations—like conservation locking—can make big difference for fish.
“This has been a really exciting year,” he says. “The results have far exceeded our expectations. This could be a real turning point for shad conservation, and for restoring migratory fish to our rivers.”
Opinions expressed on Cool Green Science and in any corresponding comments are the personal opinions of the original authors and do not necessarily reflect the views of The Nature Conservancy.